The present inventor has previously proposed U.S. Pat. No. 5,211,448 as a center lock device for preventing the stealing of automobile wheels while increasing the efficiency of automobile wheel mounting and dismounting exchange operation and while eliminating the uneasiness about the mounted state of wheels.
In the embodiments shown in FIGS. 1 through 9 of this known invention, a male thread 21 or 21a is cut in a relatively thin solid center shaft portion 20 or 20a extending from the center of an adapter A and a collar C for locking a wheel disk D is slid on said shaft portion 20 or 20a, whereupon a small-sized center lock nut N is threadedly engaged with said male thread 21 or 21a and tightened to press against the collar C from the front. The center shaft portion 20 or 20a is centrally formed with a female thread 22 or 22a which differs from said male thread 21 or 21a in the spiral pitch P1 or P2 and in the direction of spiral and a cap bolt B is screwed into said female thread 22 or 22a from the front, said cap bolt having a head 33 or 33a of large diameter which restrains said center lock nut N from slipping off.
According to the arrangement of such known invention, relatively commonplace small-sized parts can be employed as the center lock nut N and the cap bolt B for preventing said nut from slipping off, and the employment of such small-sized parts visually limits less the front surface of the wheel disk D, leaving an ample area thereon to form various ventilation patterns for heat dissipation on the wheel disk D and allowing the spokes serving as supports for the wheel rims to look as great in length as possible.
However, the center shaft portion 20 or 20a extending forwardly from the center of a conical barrel 19 or forming a top hat type or cylinder hat type adapter A is itself relatively thin, with the result that rotational bending stress produced during use with the wheel mounted repetitively concentratedly acts on said center shaft portion; thus, there is not without the danger of the center shaft portion 20 or 20a breaking off at its proximal end, or the so-called neck break accident, leading problems of decreased durability and decreased safety of the wheel attached state. Even if that is the case, however, thickening the center shaft 20 or 20a would reduce the aforesaid advantages.
Further, the above-mentioned known invention has paid no special attention to adjustment of the wheel offset (the clearance between the wheel disk attaching surface relative to the axle hub and the equator line of the wheel rim).
Therefore, in the case of the arrangement of the known invention, in adjusting the offset according to the type of the automobile, there is no other way to do this than preparing in advance various types of wheels which differ in offset or preparing in advance various types of adapters A whose joint flange 23 or 23a differs in thickness and selectively using them. However, this approach is still disadvantageous in that it is expensive and in that the efficiency of exchange operation is low.